Acrylic polyols are often reacted with aliphatic isocyanates to yield high-performance two-pack urethane coatings. Simple mixing of a polyol with an aliphatic isocyanate has reaction kinetics that are too slow for most ambient cure applications. Accordingly, such reactions are accelerated by the use of active catalysts, particularly organotin catalyst that accelerate the reaction enough that the desired rate of ambient cure can be achieved.
As may be expected, increasing the catalyst amounts leads to speedier cure; however this comes at the expense of work time, or pot-life, of the two-pack coating. By increasing the cure rates, the workable life of the formulated package is reduced. Accordingly, tin-catalyzed, two-pack urethane systems are formulated so as to strike a balance between cure rate and pot-life for the application of interest as determined by those skilled in the art.
The high-performance coatings industry is constantly looking for methods to improve the extension of pot-life, while obtaining enhanced cure rates. Dilution with additional solvent is one possibility, but this unfavorably contributes more VOC, and moreover, would eventually result in too low of a viscosity. One manner of achieving an altered balance of cure rate and pot-life is through the use of tertiary amines to provide the catalyst effect instead of an organotin catalyst. While generally inferior due to a much lower catalytic activity (tertiary amine systems require many fold more on a weight basis weight basis than organotin), similar pot-life may be achieved. Furthermore, the tertiary amine systems are more water sensitive and in high humidity situations, the cure may be negatively influenced.